Selective solvent separation of polychloroalkanes from monochloroalkanes



United States Patent 3,427,358 SELECTIVE SOLVENT SEPARATION OF POLYCHLOROALKANES FROM MONO- CHLOROALKANES Thomas A. Washall, Claymont, DeL, assignor to Atlantic Richfield Company, Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Filed Nov. 9, 1966, Ser. No. 592,966 US. Cl. 260-652 5 Claims Int. Cl. C07c 17/38; 301d 11/04 ABSTRACT OF THE DISCLOSURE Extraction of polychloroalkanes having from -8 to 16 carbon atoms in the molecule from monochloroalkanes having from 8 to 16 carbon atoms in the molecule utilizing dimethyl formamide as the selective solvent.

This invention relates to the extraction of polychloroalkanes from monochloroalkanes and more particularly it relates to a process for the extraction of polychloroalkanes having from 8 to 16 carbon atoms in the molecule, from monochloroalkanes having from 8 to 16 carbon atoms in the molecule utilizing dimethyl formamide as the selective solvent.

In the production of biodegradable alkylbenzene sulfonate detergents it is necessary that the alkyl group attached to the benzene ring be straight chain. A preferred method for the preparation of such detergents is to alkylate benzene with a straight chain monochloroalkane utilizing aluminum chloride as the catalyst and thereafter sulfonating the alkylated benzene. The straight chain monochloroalkanes are produced by the chlorination of straight chain alkanes, i.e. parafi'inic hydrocarbons which are generally derived from petroleum fractions.

In the chlorination of alkanes the reaction conditions are selected such that there is produced, on the unconverted alkane-free basis, a major proportion of the monochloroalkanes with only minor amounts of polychloroalkanes such as the dichloroalkanes, trichloroalkanes and higher chlorinated alkanes. If the polychloroalkanes are left admixed with the monochloroalkanes and the entire mixture is utilized to alkylate benzene, since benzene is always present in an excess, there will be produced polyphenylalkanes as well as condensed ring compounds. These com-pounds require additional processing either to remove them or decompose them into the monophenylalkanes since if the polyphenylalkanes are sulfonated there will be produced sulfonates which are inferior with respect to detergency and color.

When benzene is alkylated with the chlorinated alkane product, the unreacted alkanes are not separated from the chloroalkanes since the alkanes have from 10 to 13-14 carbon atoms generally and thus have boiling points that overlap the boiling points of the chloroalkanes derived from them. If a single carbon number alkane, for example, dodecane is chlorinated the dodecyl chlorides produced can be separated by distillation. It is not practical, however, to make detergents or the alkyl benzenes from single carbon number fractions, consequently the unreacted alkanes are left in the product which is used for alkylating. Accordingly, it is desirable not only to separate the polychloroalkanes from the monochloroalkanes, but it also is desirable that they be separated from mixtures of monochloroalkanes and alkanes.

-A method now has been found whereby the polychloroalkanes can be extracted from the monochloralkanes and from mixtures of alkanes and monchloroalkanes utilizing a selective solvent.

It is an object of this invention therefore to provide a process for extracting polychloroalkanes from admixture with monochloroalkanes.

It is another object of this invention to provide a method for extracting polychloroalkanes from admixture with alkanes and monochloroalkanes.

It is another object of this invention to provide a method for producing monochloralkanes of low polychloroalkane content.

Other objects and advantages of this invention will be apparent from the following description thereof and from the claims.

In accordance with this invention a mixture of monochloroalkanes and polychloroalkanes is extracted with dimethyl formamide to produce a rafiinate phase which is enriched in monochloroalkanes and an extract phase which is enriched in polychloroalkanes.

In a particularly preferred embodiment of this invention the mixture of unreacted alkanes, monochloroalkanes and polychloroalkanes which is obtained by the chlorination of straight chain alkanes having from 8 to 16 carbon atoms in the molecule is extracted with dimethyl formamide to produce (1) a rafiinate phase containing only a small amount of solvent with the remainder being the unreacted alkanes, the monochloralkanes, and an amount of polychloroalkanes which is in a greatly reduced amount as compared with the original charge mixture and (2) an extract phase containing the major proportion of the solvent 'with only small amounts of alkanes and monochloroalkanes but a high proportion of polychloroalkanes as compared with the original charge mixture.

For the production of high quality detergents the straight chain alkanes which are chlorinated have from 10 to 13-14 carbon atoms in the molecule and thus the monochloroalkanes and polychloralkanes produced therefrom will have 10 to 13-14 carbon atoms also. It will be understood that in the description of this invention the term polychloroalkanes includes the dichloroalkanes and trichloroalkanes as well as the more highly chlorinated alkanes. When alkanes are chlorinated for detergent manufacture the dichloroalkanes are present in the largest amount among the polychloroalkanes. This invention is not limited to the separation of straight chain polychloroalkanes from straight chain monochloroalkanes, but is also applicable to the separation of the branched-chain compounds.

The solvent which is utilized for extracting the polychloroalkanes from the monochloroalkanes is N,N-dimethyl formamide 'which, for convenience, is referred to herein simply as dimethyl formamide. This solvent can be employed either alone or in admixture with modifiers such as Water or low molecular weight aliphatic alcohols. It is particularly desirable to use these modifiers to improve the selectivity of the solvent when branched chain compounds are being separated. In general, the amount of water or other modifier can range from 0 to 20 volume percent of the total solvent.

The weight ratio of the solvent to the mixture of alkanes and chloroalkanes may range from 0.5 :1 to 5:1. Although a considerable reduction in polychloroalkanes can be obtained in a single treat when batch treating, it

is preferred to utrllze two or more successive extractions in order to obtain the most efiicient removal of the polychloroalkane compounds. Thus it has been found that four consecutive batch treatments on a particular mixture of alkanes, monochloroalkanes and polychloroalkanes with a 1:1 weight ratio of solvent to charge in each treat gives a product which contains such a small residual quantity of the polychloroalkanes that they are no longera problem in detergent production. In addition to batch extraction processes, conventional continuous extraction processes may be employed as are well known in the selective solvent extraction art, including for example, countercurrent solvent extraction.

The extraction process of this invention is carried out by admixing the mixture of unreacted alkanes, monochloroalkanes and polychloroalkanes with the dimethyl formamide at ambient temperatures, i.e. in the range of from 50 F. to 90 F. Higher temperatures can be used with alkanes in the C to C range, however, with the C to C alkanes higher temperatures are not preferred since these alkanes and their monochloro derivatives are more soluble in the solvent and the separation is not as efficient. In general, temperatures above about 125 F. should not be used for any of the alkanes in the C to C range. At the preferred temperatures the compounds which are treated in accordance with his invention are all liquid and accordingly this is a liquid-liquid extraction process. The solvent is agitated with the material to be extracted for sufiicient time to give thorough contacting. With sufficient mixing, times as short as 2 to 3 minutes may be employed, although longer times ranging up to an hour for example may, of course, be utilized.

After mixing, the mixture of alkanes and chloroalkanes and dimethyl formamide is allowed to stand without agitation in order that it will separate into two phases. One phase, generally the upper or rafiinate layer, being rich in the monochloroalkanes and having a reduced polychloroalkane content and the other phase, the lower or extract layer, being rich in solvent and containing the extracted polychloroalkanes with only small quantities of the monochloroalkanes. This settling or Stratification time although not critical should be sulficient to permit substantially complete phase separation to occur. In general, this time may range from 5 to 30 minutes, however, 15 minutes is completely satisfactory for most extractions. It is to be noted that while agitation should be sufficient during the mixing time, agitators which are designed to produce colloidal dispersions should not be utilized since such agitation prevents the desired and necessary phase separation.

After the settling period the phases are separated from each other by conventional decantation methods. The dimethyl formamide solvent contained in the rafiinate or upper layer may either be washed with water from the mixture of alkanes and monochloroalkanes or it may be removed by distillation, preferably by vacuum stripping at low pressures if the alkanes are C or higher. If C and C alkanes are present it is necessary to water extract the solvent since the alkanes boil below the dimethyl formamide. The solvent can then be recovered from the Water by distillation. The extraction phase which contains the major proportion of the dimethyl formamide solvent may be distilled to recover the solvent for reuse in the process. It will be understood, of course, that the solvent recovered from the rafiinate phase also may be reused in the process.

The following example is provided to demonstrate the utility of the process of the instant invention as well as to illustrate a specific embodiment of the invention within the preferred conditions which have been set forth. It will be understood, however, that this example should not be construed as limiting the invention to the exact process conditions set forth therein.

4 EXAMPLE I A feed stock resulting from the chlorination of straight chain alkanes having from 10 to 13 carbon atoms in the molecule consisted of 83.9 weight percent of the C -C alkanes, 14.8 weight percent of C C monochloroalkanes and 1.3 weight percent C -C polychloroalkanes. A sample of this feed stock weighing 37.6 grams was admixed with an equal volume (46.6 grams) of dimethyl formamide. The mixture was agitated vigorously for 3 minutes at F. and then allowed to separate to two layers. These were separated by decantation and analyzed. The phase composition and yield are shown in Table I.

TABLE I A. Phase composition Wt.(g.) Percent PereentA Percent Percent DMF M PCA Ralfillflte. 36.6 5.8 30.2 13.1 0.9 Extract-.-" 47.6 93.5 4.4 1.6 0.5

B. Yield, solvent-free basis (Yield Yield Percent Percent Percent; (grns.) (wt.pereent) A MGA PCA Charge 83.9 14.8 1.3 Raflinate"- 34.5 02.0 85.2 13.8 1.0 Extract"-.- 3. 0 8.0 67. 6 24. 7 7. 7

DMF=dimethyltormamide, A=C10C13 alkanes, MCA=O10C1 monochloroalkanes, F GA Clo-C13 polychloroalkanes.

These results show that about 40 weight percent of the polychloroalkanes present in the monochloroalkane can be removed in a single stage extraction. The alkane partition coefficient which equals the weight (grams) of alkane in the extraction phase divided by the weight (grams) of alkane in the rafiinate phase was 0.07. The partition coeflicient for the monochloroalkanes which equals the weight (grams) of monochloroalkane in the extraction phase divided by the weight (grams) of the monochloroalkanes in the raflinate phase was 0.16. The partition coeflicient for the polychloroalkanes which equals the weight (grams) of the polychloroalkanes in the extraction phase divided by the weight (grams) of the polychloroalkanes in the rafiinate phase was 0.72. These coelficients show that the polychloroalkanes can be separated efiiciently from the monochloroalkanes and alkanes since the partition coefiicient for polychloroalkanes is about 4.5 times greater than the partition coeflicient for the monochloroalkanes and 10 times the coefficient for the alkanes themselves.

I claim:

1. A process for selectively extracting polychloroalkanes having from 8 to 16 carbon atoms in the molecule from admixture with monochloroalkanes having from 8 to 16 carbon atoms in the molecule which consists essentially of mixing said monochloroalkanes containing said polychloroalkanes with a solvent selected from the group consisting of dimethyl formamide and a mixture of dimethyl formamide and up to 20 percent by volume of Water at a temperature in the range of from 50 F. to F., at a weight ratio of solvent to chloroalkane mixture in the range of from 0.5 :1 to 5:1 and separating a rafiinate phase enriched in said monochloroalkanes from an extract phase rich in solvent and containing said polychloroalkanes.

2. The process according to claim 1 wherein the monochloroalkanes and polychloroalkanes have from 10 to 14 carbon atoms in the molecule.

3. The process according to claim 1 wherein the mixing is carried out at a temperature in the range of from 50 F. to 90 F.

4. The process according to claim 1 wherein the solvent is a mixture of dimethyl formamide and up to 20 percent by volume of Water.

5. The process according to claim 1 wherein the mixture of monochloroalkanes and polychloroalkanes have from 10 to 13 carbon atoms in the molecule, the mixing with solvent is at a temperature in the range of from 50 F. to 90 F. and monochloroalkanes having reduced polychloroalkane content is recovered from the rafiinate phase.

6 References Cited UNITED STATES PATENTS 2,189,924 2/1940 Pier et a1.

3,219,546 11/1965 Fannin et a1.

3,288,877 11/1966 Taylor et a1. 203-60 3,349,008 10/ 1967 Vives 203-60 FOREIGN PATENTS 1,416,405 9/ 1965 France.

LEON ZITVER, Primary Examiner.

H. I. MARS, Assistant Examiner. 

